Hi Dan, whether the plant is upgraded or not doesn't improve their system's capabilities. In other words, the potential data rate is the same in either case.
The 14Mbps capacity number that you see in press releases and trade rags is marketing hype. It misrepresents the end-to-end data capacity by some 40%. It includes all overhead, ECC, and control bits. The real number for a 100% efficiently utilized system is 8.2 Mbps divided between 128 channels. 100% efficient utilization is not practical over extended periods, but that's the achievable capacity nonetheless. Each user subscribes to one or more channels.
The system itself actually has 144 channels in each frame, but 16 channels are for control purposes (which is where the 128 channels above came from). The frame rate is 8kHz including the guard interval used for ranging (this is where the "S" in S-CDMA enters the picture), and each channel in a given frame consists of 8 bits plus 1 control bit. Each is spread by a 144 chip spreading code (the "S" enters the picture here too, since an async system would require a longer chip sequence) across the 5MHz channel they use. Real data per frame per channel is 64kbps (which is how they partition it out to subscribers). The total data rate per 5MHz channel with ¾ rate trellis coding is: (128+16) * ([8+1]*8kHz) * 4/3 =13.8 Mbps (which is the often quoted 14 Mbps number). The Real data rate (not counting any of the overhead stuff) is 128 * (8 * 8 kHz)=8.2 Mbps.
I won't even go into the downstream rates, but they're not at all comparable to, for example, DOCSIS 1.0/ J.83 Annex B PHY, in even the lowest performance configuration. Remember, though, the DOCSIS system is on upgraded plant so on DOCSIS turf, the TERN S-CDMA as described in their patents really doesn't match up. That was my main point--that it's applications are numbered.
Also, be careful with comparisons and analogies with CDMA in the wireless world. Most of the comparisons aren't valid. The similarities are only at the highest of levels (i.e. the types of things you see in Powerpoint presentations). Cable is a very different operating environment. CDMA is not the best solution for everything, despite what SOME would have you believe<gg>.
dh |
